ct vs mri

Re: ct vs mri

Alex Gough — Wed, 12 Jan 2011 09:11:21 GMT

There are permanent on site MRI and CT local to Patrick, and if it's urgent then getting a CT scan done if the dog won't fit in the permanent MRI scanners may be preferable to waiting, especially for spinal work. If it is non-urgent, Langford have a high field MRI scanner weekly that can fit big dogs.

Alex

Re: ct vs mri

Rob Loxley — Fri, 07 Jan 2011 20:19:31 GMT

[quote user="patrick murphy"]is too big for a MRI so I should CT?just because he fits?[/quote]

you just need a bigger MRI scanner

Re: ct vs mri

patrick murphy — Fri, 07 Jan 2011 14:08:01 GMT

so the 25 kg Basset that I am treating now, if he does not respond, is too big for a MRI so I should CT?just because he fits?

Re: ct vs mri

Alex Gough — Thu, 06 Jan 2011 11:12:39 GMT

[quote user="Malcolm Ness"]Beware the low field MRI scanner driven by a vet with no proven imaging or neurological expertise - some of them will have you believe that it isn't safe to give a worming tablet unless they have first scanned the patient!![/quote]

I knew I would be glad I did a postgraduate certificate in neuroimaging!

Alex

Re: ct vs mri

Malcolm Ness — Thu, 06 Jan 2011 09:13:52 GMT

Excellent summary from Alex.

We have on site CT and visiting (high field) MRI. Considered installing one of the low field MR units but decided against as we have got used to the superior image quality and somewhat shorter accquisition times.

There remains some considerable controversy about CT vs MRI in spines. Imagers point out that MR gives better soft tissue image and while this is true of well performed high field MR, which is costly and very time consuming, experienced clinicians prefer CT because it is quick, cost-effective and the info provided by CT and CT myelography (on top of the standard examinations) correlates very closely with what we can treat mediacally or surgically. A couple of papers recently have implied that the additional detail provided by MR does is not of any clinical benefit in terms of case management. ( I think one came from London with C Lamb as an author and another from Kirbergers group in SA).

Our "routine" spinal cases get a thorough clinical assesment including a detailed neuro exam before CT myelography - quick, cost effective and produces clinically relevant diagnostic info.

Similarly, (MRI and CT) can produce some really pretty pictures of the cruciate ligaments and menisci but when our understanding of the pathology and our options/ability to treat stifle joints remains as limited as it currently is, these images are at best a research tool, and at worst a clinicians plaything.

Beware the low field MRI scanner driven by a vet with no proven imaging or neurological expertise - some of them will have you believe that it isn't safe to give a worming tablet unless they have first scanned the patient!!

Re: ct vs mri

Alex Gough — Wed, 05 Jan 2011 16:30:50 GMT

I agree with Andrew It is without question the modality of choice for imaging brains (except in acute head trauma where early bleeding is picked up more reliably by CT, and the shorter image acquisition time is useful there too. Also skull fractures are better seen on CT). MRI is also the modality of choice for imaging the spinal cord, although CT can be useful, especially for imaging the vertebrae. However, here you have to be a little cautious in choosing the type of scanner you select. We have a low field scanner, permanently on site, which gives great images of brains and noses, and gives good images of small dog spines, and cervical and lumbo-sacral regions of larger dogs. However, due to the field of view, and other technical factors, large dogs thoracic spines may be harder to image, and a high field scan (in most places intermittently available as a mobile service, but some places have on-site high field scanners like Willows and AHT) can give much better pictures. We are soon getting a new spinal coil for our machine which might help with some of these issues, but probably not all of them.

Other uses for MRI: surgical planning of invasive soft tissues tumours, provided they are not in a moving part of the body, retrobulbar lesions, certain orthopaedic applications (meniscal damage, partial cruciate tears), imaging of the pelvic and retroperitoneal regions.

CT is generally superior for most orthopaedic applications. Because of its fast acquisition time, it is the only modality really suitable for imaging the chest, unless using certain sophisticated MRI techniques such as cardiac and respiratory gating (and I'm not sure if anyone is in the UK veterinary field), and will generally give a superior image to MRI when looking at the abdomen.

So in summary

MRI: brain, spine, nose, retrobulbar, certain soft tissue tumours

CT: bone, chest, abdomen, certain soft tissue tumours

Either: pelvis, retroperitoneal space

Alex

Re: ct vs mri

Rob Loxley — Tue, 04 Jan 2011 23:58:32 GMT

In Practice 2003 25: 243-254:
Advanced imaging: indications for CT and MRI in veterinary patients
Ruth Dennis

Re: ct vs mri

Andrew Kent — Tue, 04 Jan 2011 15:01:29 GMT

[quote user="Michael Woodhouse"]

CT uses xrays so good for bone.

MRI better for soft tissue

[/quote]

That is true to some extent but unfortunately acquisition time is also an important consideration. MRI has a very long acquisition time so is no good for areas that move (chest/abdo) but excellent for areas that are fairly immobile. We use MRI mainly for brains, spines, noses, necks things like that. CT we primarily use for chests with the occasional abdomen. I know elsewhere CT is used for orthopaedic planning for complex fractures but haven't seen much of that yet.

Andy

Re: ct vs mri

Michael Woodhouse — Tue, 04 Jan 2011 14:00:19 GMT

CT uses xrays so good for bone.

MRI better for soft tissue